1. Field of The Invention
This invention relates to a semiconductor device and a method of manufacturing thereof and particularly it relates to a semiconductor device having an opening region for interconnection and a method of manufacturing thereof.
2. Description of the Prior Art
Aluminum and aluminum alloys are conventionally utilized as materials for an electrode and interconnection film of a semiconductor such as silicon. However, according to the recent trend toward high density and large scale integration of semiconductor devices, it becomes more and more difficult to cover a step portion of a contact hole in a semiconductor device.
FIG. 1 is a view showing a sectional structure of a conventional semiconductor device. Referring to FIG. 1, an oxide base film 2 is formed on a silicon substrate 1. A smooth coat film 3 of phospho-silicate glass is formed on the oxide base film 2. This semiconductor device is provided with a contact hole 9 for interconnection of the device. Further, an electrode and interconnection film 4 of aluminum or aluminum alloy is formed to cover the contact hole 9.
Next, a method of manufacturing of the conventional semiconductor device shown in FIG. 1 will be described. A film of Al-Si is formed by a sputtering process over the whole surface including the contact hole 9 in the silicon substrate 1 and the smooth coat film 3. At this time, the wafer is generally heated for the purpose of attaining a good state of the coverage of a step portion 5 having a level difference.
Then, patterning of the resist is made by a photolithographic process. Subsequently, unnecessary portions of the Al-Si film are removed by etching so that the electrode and interconnection film 4 including an external electrode outlet region (not shown) is obtained. Then, heat treatment at about 450.degree. C. is applied so as to make an electric contact between the electrode and the silicon substrate 1 and to increase stability of threshold voltage of the transistor.
FIG. 2 is a graph showing hardness of different kinds of connection layers. If heat treatment is applied after an Al-Si connection layer 4 of about 1 .mu.m in thickness for example has been formed in a conventional semiconductor device manufactured by the above described manufacturing process, the Knoop hardness becomes as low as about 30HK as shown in (a) of FIG. 2.
Particularly, because of the recent tendency to increase a chip size of an LSI, transformation of a connection region is liable to occur due to contraction stress of a mold material.
As for dependency of film hardness on Ti density before and after the heat treatment of an Al-Si-Ti layer, a description thereof is given for example in "Al-Ti and Al-Ti-Si Thin Alloy Films" by Albertus G. Dirks et al. in J. Appl. Phys., Vol. 59, No. 6, Mar. 15, 1986, pp. 2010-2014. In addition, "Stress Analysis of Passivation Film Crack for Plastic Molded LSI Caused by Thermal Stress" by Okikawa et al. in International Symposium for Testing and Failure Analysis 1983, pp. 275-280 indicates evaluation of pressure of a mold and strength of an aluminum connection layer in a chip. However, none of those documents discloses a connection layer having a high degree of hardness which can be maintained after heat treatment.